Polypedilum vanderplanki only inhabits semi-arid regions of Africa, and is the only insect whose larvae can resume normal growth within one hour of being placed in water for absorption even after 48 hours of complete dehydration (Watanabe, M., Kikawada, T., Minagawa, N., Yukuhiro, F., and Okuda, T. (2002) J Exp Biol 205, 2799-2802). This state, in which the organism can recover even after complete desiccation, is called cryptobiosis. After entering a cryptobiotic state, P. vanderplanki can survive at temperatures from −270° C. to +102° C., or in 100% ethanol (Hinton, H. E. (1960) J Insect Phys 5, 286-300; and Hinton, H. E. (1960) Nature 188, 336-337). Trehalose has been said to be essential to inducing and maintaining the cryptobiotic state. However, even when desiccation occurs after accumulating a high concentration of trehalose in the body, there are some cases when the cryptobiotic state is not achieved (Watanabe, M., Kikawada, T., and Okuda, T. (2003) J Exp Biol 206, 2281-2286). Since trehalose accumulation alone is insufficient to explain the mechanism of cryptobiosis induction and maintenance, factors other than trehalose should be necessary for cryptobiosis.
The dormancy of plant seeds is a type of cryptobiosis. Seed dormancy occurs in late embryogenesis, and for approximately 20 years, proteins called late embryogenesis abundant (LEA) proteins have been known to accumulate specifically during this period (Dure, L., 3rd, Greenway, S. C., and Galau, G. A. (1981) Biochemistry 20, 4162-4168; Grzelczak, Z. F., Sattolo, M. H., Hanley-Bowdoin, L. K., Kennedy, T. D., and Lane, B. G (1982) Can J Biochem 60, 389-397). Under desiccation stimulus, expression of these proteins is increased not only in seeds, but also in pollen and in plant bodies (Ingram, J., and Bartels, D. (1996) Annu Rev Plant Physiol Plant Mol Biol 47, 377-403). LEA proteins have characteristic secondary structures and share an α-helix-rich structure (Goyal, K., Tisi, L., Basran, A., Browne, J., Burnell, A., Zurdo, J., and Tunnacliffe, A. (2003) J Biol Chem 278, 12977-12984). The results from transgenic yeast and rice have revealed that these proteins show stress-resistant functions such as desiccation resistance, cold resistance, and salinity resistance; however, the detailed biochemical functions (activities) of the proteins themselves are still unknown (Wise, M. J., and Tunnacliffe, A. (2004) Trends Plant Sci 9, 13-17). These proteins were thought to exist exclusively in plants. However, following their discovery in nematodes in 2002 (Browne, J., Tunnacliffe, A., and Burnell, A. (2002) Nature 416, 38), the existence of LEA proteins in organisms other than plants has been strongly suggested.